What is the cause of a number four cylinder misfire on a 2004 BMW 325i?

Answer 1

There are multiple things that can cause a missfire on this engine. The ussual issue is the ignition coil. Remove it and check to see if it is a Bremi made coil or a Bosch made coil. The Bosch style coil has a silver linning around the lower boot portion. If it is a Bosch style it is unlikely that the coil went bad, if it is a Bremmi coil you need to go to the Dealer and have the coil replaced for free under a recall that BMW had for the Bremmi coils. If the coil is not the issue you need to check the spark plug, especially if it is a manual trans. Look at the white part of the plug for black(carbon) lines up and down on it, then check the gap of the plug. If that all checks out well and the vehicle only runs rough while cold you most likely have an issue with the lifters under you camshafts. This is not a job to be done by anyone other than a professional. Also the lifters repair may include the replacement of the camshaft itself also and this is no cheap repair.